This invention relates to a fastener for quickly and securely fastening a bone plate to surrounding bone. In one embodiment, the fastener contains a torque-limiting feature to prevent over tightening when in the fastening position. In another embodiment, the invention relates to an instrument for applying the fastener to a bone plate and surrounding bone.
When performing surgery on the brain, it is often necessary to perform a craniotomy to provide access to portions of the brain. A craniotomy is a surgical procedure in which a portion of the cranium is removed to permit access to the brain. To perform the craniotomy, one or more holes are initially drilled through the skull. These holes, known as xe2x80x9cburr holes,xe2x80x9d may be located, for example, at the corners of a triangular region of bone that is to be temporarily removed. A saw, i.e., a craniotome, is then used to cut the skull along the line of separation connecting the adjoining burr holes. The resulting bone cover or bone plug is subsequently lifted from the underlying dura matter to expose the brain. The bone cover may either be completely removed from the cranium, or folded back in a flap along an uncut edge of the flap.
After completion of the procedure on the brain, the bone cover must be re-attached to the skull. Several devices have been developed that are used to facilitate securing the bone cover to the skull. These devices suffer from the disadvantage that they are cumbersome or inefficient to apply to the bone flap and surrounding bone. Further, prior designs are relatively rigid, thus decreasing conformance to the curvature of the skull. Moreover, prior designs often required significant instrumentation to apply and/or adjust the device used to secure the bone cover to the skull. Finally, prior designs may require removal of the fastening device after sufficient healing along the line of separation.
The Cranial Clamp And Method For Fixating A Bone Plate according to the invention generally includes a cap and base adjustably joined by a post for threadably bringing the opposing cap and base closer together, thereby tightening them against the internal and external surfaces of the bone plate and surrounding cranium. The base and cap securely fix the bone plate to the surrounding bone. In one embodiment, at least one of the base, cap and post include resorbable material.
The clamp according to the invention may further include an applier interacting with the post to position the cap and base to securely fix the bone plate to the surrounding bone. Once appropriately secured, the applier is removed from the post while leaving the cap and base interconnected. In one embodiment, the applier includes a keyed bore and the post includes a key for engaging the keyed bore of the applier.
The clamp according to the invention may also include a torque-limiting feature on the post. The torque-limiting feature prevents stripping of the threaded interconnection between the post and cap or overtightening of the cap relative the base. In one embodiment, the torque-limiting feature is disposed at a junction between an elongated body portion and a keyed portion of the post.
The method for fixating a bone plate in a bony defect according to the invention allows a bone plate to be fixed in apposition against a transverse face of surrounding bone along the border of junction between the bone plate and surrounding bone. A base connected to an elongated externally threaded post projecting from the base, and a cap with an internally threaded collar for mating and threaded engagement with the threaded post connected to the base, is provided. In one embodiment, at least one of the base, cap, and post include resorbable material. The base and cap are placed on opposing internal and external surfaces of the bone plate, with a portion of each of the base and cap overlapping the border of junction. The post is rotated into the collar to bring the base and cap to a fastening position having the base and cap in tight engagement against the opposing internal and external surfaces of the bone plate. At least one of the base, cap, and post include resorbable material, which is resorbed by the body.
The method according to the invention may further include providing an applier, wherein the applier rotates the post through inter-engagement of the applier with the post. The method according to the invention may also include removing a distal portion of the post projecting from the cap and leaving a proximal portion of the post projecting from the cap. Moreover, the proximal portion of the post projecting from the cap may be deformed to secure the base and cap in the fastening position.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.